imsak

Salam AlaykumI've heard a few islamic rulings that beginning the fast in ramadan at an appointed/calculated time before fajr.. known as imsak - is islamically wrong. ive unknowingly been using the time of imsak to begin fasting for years now. So I would like to know the proper ruling on imsak if it is valid or not- and if it is correct to fast from fajr onwards, also please clarify all sources of information. thankyousalam

Dear scholars, As-Salamu `alaykum. I misunderstood the imam when I asked about the time of imsak (abstaining from food and drink, etc.). I just found out that imsak is 15 minutes before fajr (dawn), but most of the days this Ramadan I ate a few minutes before fajr, as well as in Sha`ban when I was making up for the days I had missed during the previous Ramadan (due to menstruation). Please tel l me if I should make up for these days of Ramadan as well as the days I had made up in Sha`ban for previous ones. Jazakum Allah khayran.